The present invention relates to a hard disk drive having an error correcting function.
Conventional hard disk drives have a rotatable disk-shaped recording medium, and data are recorded on concentric tracks arranged on the recording medium. Usually, a magnetic material is used in the recording medium (hereinafter referred to simply as "medium") in view of cost, storage capacity, etc. However, it is impossible to manufacture a medium which can provide a 100%-perfect recording state. As a countermeasure, an error correction code (hereinafter referred to as "ECC") is added to the data to enable correction of a possible recording error at a certain location on the medium to provide a virtually perfect recording state. Thus, clearing various requirements for cost, storage capacity, etc., the medium is now put into practical use.
FIG. 2 shows a fundamental constitution of the above type of conventional hard disk drive. In FIG. 2, reference numeral 20 represents a hard disc drive (HDD); 10, a computer main body for controlling the hard disk drive 20; 11, a bus line for devices that conform to standards of SCSI etc.; and 30, another hard disk drive (HDD). The hard disk drive 20 includes a bus interface 21, a controller 22, a track address register 23, a head arm drive circuit 29, a read/write head arm 24, a medium 25, a read/write circuit 27, and a serial/parallel conversion circuit 28.
With the above constitution, in accordance with a write instruction sent from the computer main body 10 to the hard disk drive 20 via the bus line 11, the data is written to the proper track on the medium 25.
More specifically, the write instruction is provided to the controller 22 via the bus line 11 and the bus interface 21, and a track address indicating a writing location on the medium 25 is provided to the track address register 23 and retained therein. Receiving the track address, the head arm drive circuit 29 drives the head arm 24 under the control of the controller 22 so that a read/write head is positioned on the proper track.
Upon completion of the mechanical operation, parallel write data is sent from the computer main body 10, and converted to serial data by the serial/parallel conversion circuit 28. The ECC of, for instance, 88 bits that is calculated from the serial data is added to the serial data, and the ECC-added data is written to the proper track.
Although the synchronization with the rotational phase of the medium 25 is actually taken, a head drive mechanism, medium rotational drive mechanism, etc. are neither illustrated nor explained here for simplification of the description.
Then, in accordance with a read instruction sent from the computer main body 10 to the hard disk drive 20 via the bus line 11, the data recorded on the subject track on the medium 25 is read.
More specifically, the read instruction is provided to the controller 22 via the bus line 11 and the bus interface 21, and a track address indicating a reading location on the medium 25 is provided to the track address register 23 and retained therein.
Receiving the track address, the head arm drive circuit 29 drives the head arm 24 under the control of the controller 22 so that a read/write head is positioned on the proper track.
Upon completion of this mechanical operation, the read/write circuit 27 reads, via the head, the ECC-added data recorded on the subject track. The ECC-added data may include a recording error originating from the medium property etc. To accommodate such a case, the original data is calculated back and reproduced from the ECC-added data using the ECC that has been added to the data. The ECC has the restoration ability proportional to the number of bits, and original data having only slight errors can be completely restored. Even in many of the cases where the data restoration is impossible, the error detection is possible.
The serial data thus read and restored is converted by the serial/parallel conversion circuit 28 to parallel data that conforms to the standard of the bus line 11, and the parallel data is provided to the computer main body 10.
The read/write circuit 27 writes to the medium 25, the data which has been given the ECC, and the original data is calculated back and reproduced from the ECC-added data read from the medium 25. In this manner, the write and read operations of the hard disk drive 20 can be performed with a high accuracy.
As described above, to use the medium that cannot be 100%-perfect, the conventional hard disk drive realizes the error correcting function by recording the ECC-added data and provides cost reduction, high-density recording, etc.
Although necessary for the error correction, the ECC is redundant information unlike the data proper and reduces the storage area of the medium available for the data. Therefore, the quantity of the ECC should be as small as possible.
On the other hand, since the medium is a rotational disk, the probability of the error occurrence is different in the inner tracks and in the outer tracks; that is, usually the error occurrence is less likely in the outer tracks. Further, it may frequently be the case that due to variations in the manufacturing process, materials, etc., individual media have different tracks which are likely to be associated with an error.
However, the conventional hard disc drives employ the ECC having the number of bits that corresponds to the general probability of error occurrence at the innermost track in which an error is most likely to occur. And the ECC having the same number of bits (i.e., excessively redundant) is added to the data that is to be recorded on the outer tracks in which the error occurrence is relatively unlikely. This is not preferable because the storage capacity of the medium is consumed vainly as much.